Children ages 3 and 4 know that sharing is the right thing to do, but they haven't developed the moral skills to act on it, a study finds. But most children learn to do so within a few years.

The study set out to explore the development of children's moral decision-making. (Los Angeles Times )

What parent of a young child has not experienced the stinging shame of seeing her sweet toddler — who knows all too well that sharing is the right thing to do — yank a favorite toy from a playmate and retreat to a corner where he can have it all to himself?

Take heart, a new study finds. Your admonishments to share have been heard and absorbed. It's just that, at ages 3 and 4, a typical toddler hasn't yet developed the moral decision-making skills that align his behavior with what he knows is right.

In children who are 5 or 6 years old, that moral compass is still a work in progress, according to the study. But by 7 or 8, even the most covetous kid will probably have learned to weigh "I should do the right thing" more heavily than "I really, really, REALLY don't want to share."

The study, published Wednesday in the journal PLOS ONE, set out to explore the development of children's moral decision-making. Researchers quickly focused on toddlers' long-observed and much-bemoaned penchant for claiming coveted items for themselves.

Armed with rolls of scratch-and-sniff scented stickers, researchers ran a series of experiments on 102 children ages 3 to 8 to discern why hoarding behavior happens, and when and why it stops.

What they found should encourage parents who fear their grabby toddler has paid no attention to their moral guidance, that he is too impulsive to obey or that he is a psychopath in the making.

The researchers discovered that 3- and 4-year-olds are aware that sharing their stickers is the right thing to do. And they optimistically believe that other children their age will do so generously.

But when asked to hand over some of their windfall of four stickers, many refused to do so and most of those who did offered up only one. Among the 7- and 8-year-olds, nearly all split their stickers evenly. (The 5- and 6-year-olds fell somewhere in between.)

"Over time, it went from being a discussion about satisfying their own desires to talking about what makes people happy and what's fair," said Craig E. Smith, lead author of the study and a postdoctoral fellow at the University of Michigan's department of psychology.

Nicolas Baumard, a researcher at the University of Pennsylvania who was not involved with the study, said that despite evidence of toddlers' hypocritical behavior, "it is possible that we might still underestimate children's moral abilities."

Other studies have found that when children collaborate in pairs, they are much more generous with their partners, he said.

Indeed, recent research in this burgeoning field of developmental psychology has shown that very young children behave more altruistically when others are looking.

"It could be argued that increases in fair-sharing are due to children's developing concern for their moral reputations," Smith and his colleagues wrote. "Children remain self-interested at all ages, but with age, they become more aware of the fact that other people's opinions of them matter."